1. Field of the Invention
This invention relates to multimedia communication networks, such as TV cable systems, that send both broadcast and on-demand features to a number of subscribers, wherein each subscriber location includes a set-top terminal and a television (TV) set that is connected to the set-top terminal. More specifically, this invention relates to a cable TV system wherein system-authorized set-tops are constructed and arranged to reconstruct scrambled TV transmissions or TV pictures independent of a prior knowledge of the method or algorithm by which an unknown and proprietary scrambling system has operated to scramble the TV transmissions that are received by the authorized set-tops.
2. Description of the Related Art
An early commercial installation by Warner Communications Company, under the brand name QUBE, provided an interactive television system.
On demand, interactive, television systems are known in the patent art. U.S. Pat. No. 5,412,720 to Hoarty, U.S. Pat. No. 5,093,718 to Hoarty et al, and U.S. Pat. No. 5,361,091 to Hoarty et al, incorporated herein by reference, are examples.
Video inversion scrambling systems are known and are currently used in most cable TV systems for the purpose of scrambling analog TV signal channels prior to transmission to the set-tops within the cable system. This TV signal scrambling prevents unauthorized subscribers from receiving and viewing the scrambled TV programming. As a scrambled channel is received by an authorized subscriber, that set-top terminal, having a compatible descramble function therein, enables the authorized subscriber to view the programming on a local TV set, usually at an additional cost to that subscriber. An example of the need for subscriber authorization, sometimes called conditional access, is in the well known pay-per-view or view-on-demand industry.
U.S. Pat. No. 4,222,068 to John R. Thompson, incorporated herein by reference, is an example of TV signal scrambling. In this patent, a subscriber TV system comprises a video encoder means for randomly inverting the polarity of a trace line of randomly selected vertical intervals, and by inverting the trace lines of associated fields following the randomly selected vertical intervals, the encoder means further including means for suppressing the amplitude of randomly selected horizontal blanking pulses during the fields of the video signal that form a scrambled video signal.
Another example is shown in FIG. 1 wherein cable TV system 10 includes a TV picture source 11 and a proprietary scrambler 12. In this example, scrambler 12 is proprietary to a third party herein referred to as vendor-A. Scrambler 12 operates to scramble the TV transmission or picture signals that are transmitted on channels 13, thereby preventing unauthorized subscribers from receiving and viewing the scrambled TV programming that is transmitted on channels 13. In FIG. 1, the system subscribers are represented as a plurality N of set-tops 1 through N. Each of the N set-tops is uniquely addressable, as is well known to those of skill in the art.
In FIG. 1, set-top 1 is seen as receiving a viewing-authorization, or permission-to-descramble, signal 14 from cable system 10, this signal being addressed only to set-top 1. As a scrambled channel 13 signal is received by the authorized subscriber having set-top 1, descrambler 15 enables set-top 1 to view that programming on its local TV set 16. While not shown, each set-top in the system also receives an encrypted message that provides each authorized set-top with the scramble-key. This key enables each authorized set-top to descramble the scrambled signal channel 13 signal.
Such a scramble/descrambler video inversion system is usually proprietary to the stated vendor-A that provides the set-top terminals 1-N to the operator of cable system 10. More particularly, each of the N set-tops contains a proprietary controller that includes the descramble function 15.
In the event that the operator of cable system 10 decides to change the vendor of its set-tops, for example, from vendor-A to a new vendor-B, then the cable system operator is faced with the problem of completely changing all set-stops to the new vendor-B, or in one way or another, the scramble/descramble system of vendor-A must be reverse-engineered, and vendor-B must install a system that is compatible with the proprietary system of vendor-A, thereby providing a cable TV system 10 that comprises a mix of set-tops manufactured by vendor-A and manufactured by vendor-B.
The present invention fills the need in the art for a cable system that enables a set-top manufactured by any vendor to, upon proper receiving authorization, reconstruct scrambled TV pictures, regardless of the proprietary scrambling system that was used to initially scramble the TV pictures. The construction and arrangement of the present invention operates to provide similar security to that of the original cable system in that only authorized set-tops are enabled to view or descramble the TV pictures.